MANKATO, Minn. -- When Antoine Winfield took less guaranteed money to sign with the Seattle Seahawks instead of rejoining the Minnesota Vikings this offseason, a gap surfaced in the defense that rivaled the exodus of Percy Harvin on offense.

Coach Leslie Frazier said he wants cornerback Xavier Rhodes to make an immediate impact and possibly start alongside Chris Cook as the base corners, but what about Winfield's nickel spot?

"There's a hole there we have to fill," said Frazier on Friday after the Vikings' first day of training camp. "There's some pieces in place, but there's unknowns. We have to get reps under our belt and preseason games so we can evaluate them."

Josh Robinson, in his second year out of Central Florida, is the budding candidate at nickel cornerback and has received the first-team reps in that spot so far this offseason.

Like many other pieces on this team, Robinson needs to take a step forward from how he played as a rookie - tentative at times, allowing seven of every 10 passes thrown his way to be caught and ultimately giving up six touchdowns.

"I have to eliminate the deep ball," Robinson said. "I gave up some touchdowns last year and I have to eliminate those completely."

The Vikings are returning every piece -- sans Winfield, plus Rhodes -- in a secondary that finished 24th in the league for passing yards allowed.

The Vikings' secondary can't hide in a division with no pushovers in the passing game - quarterback Aaron Rodgers in Green Bay and stud receivers in Chicago's Brandon Marshall and Detroit's Calvin Johnson.

Frazier said he believes the Vikings' secondary will come together on its own, without any additional help.

"We think Josh [Robinson] will do a great job for us, hope Chris [Cook] stays healthy and continues to mature and we'd like to see Xavier [Rhodes] come along fast for us," Frazier said. "We think A.J. [Jefferson] will do a good job for us."